James Thurber's story "The Secret Life of Walter Mitty" is very short: 15 paragraphs, barely 2,000 words. You can read it (or reread it) in less than 10 minutes: a small and sad-eyed daydream, much like the action it describes.

And yet, since it first appeared in the March 18, 1939, issue of the New Yorker, Thurber's small-bore masterpiece has inspired two full-length films: the 1947 version with Danny Kaye and a new adaptation, due in December, starring and directed by Ben Stiller. The first trailer has just been released, and it suggests something of the challenges of developing any work of short fiction (and, perhaps, especially this one) into a film.

Stiller's Walter Mitty, after all, appears to be based on Thurber’s character in name only: A solitary photo editor at Life magazine (a magazine editor? There’s a daydream), he pines after a co-worker, played by Kristen Wiig, and eventually reconciles his secret inner life by asserting himself in the “real” world.

This recalls the earlier adaptation, in which Kaye, as Mitty, also steps outside himself, getting enmeshed in an adventure involving stolen jewels. I understand the logic — you need action in a movie — but I can’t help thinking that it’s antithetical to what the story is about.

For Thurber, Mitty is a tragic figure … or no, not tragic, because that would imply a stature that he doesn’t have. The entire story takes place over the course of an afternoon, as Mitty — henpecked, never fully present — drops his wife off at the hairdresser and then runs a couple of errands (buying overshoes and dog biscuits) before meeting up with her again in the lobby of a hotel.

He is lonely, lost, an anonymous man of middle age whose fantasies (Navy pilot, brilliant surgeon) are triggered by his glancing interactions with the world. Thus, a set of photos in Liberty magazine “of bombing planes and of ruined streets” (it was the dawn of World War II) leads Mitty to imagine himself as an Army captain on a suicide mission at the front. “It’s forty kilometers through hell,” a sergeant tells him. “[W]hat isn’t?” Mitty replies.

That, to me, is the center of the story, which is less about redemption than it is about resignation, about the imagination not so much as refuge as retreat. Unlike Nik Worth, whose elaborate rock star fantasies drive Dana Spiotta’s 2011 novel "Stone Arabia," Mitty’s inner landscape is no richer than his day-to-day existence; he is not enlarged by his dreams but only reminded of how small he is.

Even at story’s end, when he pretends that he is bravely awaiting execution, it is cliché that moves him, the stuff of Hollywood, and not of life.

“To hell with the handkerchief,” Mitty imagines saying. Thurber continues: “He took one last drag on his cigarette and snapped it away. Then, with that faint, fleeting smile playing about his lips, he faced the firing squad; erect and motionless, proud and disdainful, Walter Mitty the Undefeated, inscrutable to the last."